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Re: Vertical Lines (Boundaries)

  • To: mathgroup at
  • Subject: [mg4818] Re: Vertical Lines (Boundaries)
  • From: Harald Berndt <hberndt9 at>
  • Date: Fri, 20 Sep 1996 01:12:40 -0400
  • Organization: IDT Corporation
  • Sender: owner-wri-mathgroup at

Larry Smith wrote:
> After talking to Tech Support today I was able to get a short term fix for
> a problem that I have encountered.
> Example:  Plot the equation y=x^2 and show boundaries at x=1 and x=2
> (vertical lines).  Is there an easy way to do this?
> The problem could also be asked where you need to use implicit plotting
> ImplicitPlot[x=y^3,{x,0,3}] and have y horizontal lines at y=1 and y = 2.
> Any suggestions?
> So far I only have the following:
> Show[Graphics[Line[{{1/2,-1,{1/2,8}}]], DisplayFunction -> Identity]
> Plot[x^2,{x,0,2},DisplayFunction -> Identity]
> Then combine the previous Out[] which in this case was Out[10] Graphics,
> and Out[11] Graphics
> Show[%10,%11, DisplayFunction -> $DisplayFunction]

Needing many customizations of plot output, I have really come to 
appreciate the Epilog and Prolog options available in all (I think) 
plotting functions. In your example, you could simply render the lines 
you need by

     ImplicitPlot[yourEquation,yourDomain, Epilog ->
          {Line[{startPt, endPt}]


     ImplicitPlot[yourEquation,yourDomain, Prolog -> {

Prolog is the better choice if you specify style options to 
distinguish border lines and graph and want the graph to be _in front_ 
of the border lines (Prolog directives are rendered before the rest of 
the plot). Example:

ImplicitPlot[x == y^3,{x,0,3},
	PlotStyle -> {GrayLevel[0],
	Prolog -> {
		GrayLevel[0.5], Thickness[0.01],
		Line[{{.5, -1}, {.5, 8}}],
		Line[{{2, -1}, {2, 8}}]

(Note that you'll have to specify PlotStyle in the plot, otherwise the 
graph will be rendered with the styles set in the Prolog.)
Harald Berndt, Ph.D.                              Research Specialist,

Phone:	510-652-5974                                FAX:			510-215-4299
"I yam what I yam"...................................Popeye the sailor
(Kryten:............"I thought that was Descartes!"..................)
(Lister:............"So did I. mon, so did I!".......................)


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